A hard disk drive (HDD) that functions as a disk apparatus includes a rectangular casing, a disk-like recording medium disposed within this casing, and a magnetic head disposed within the casing for reading or writing data from or to the recording medium. The casing includes a rectangular base, a plate-like top cover screwed onto the base, and a packing member (e.g., gasket) disposed between a peripheral portion of the base and the top cover.
In such an HDD, a portion of a sidewall of the base which is adjacent to the magnetic disk is made thinner due to a dimensional restriction. An HDD having a large height, in particular, has a sidewall that is thin and high. Owing to this, when the base that has such a sidewall is aluminum or the like, reliably forming the sidewall via die cast molding is difficult. Furthermore, in the portion of the sidewall that is thinner in wall thickness, it is difficult to sufficiently secure a width of a surface in contact with the gasket, which can make formation of an airtight seal problematic.